The present invention relates to a resist material sensitive to activation rays. More particularly, the present invention relates to a radiation-sensitive mixture for use in the production of semiconductor elements and masks, having high sensitivity and high resolution, capable of being applied to a method useful for the formation of both positive and negative patterns, in which an acid generated by the irradiation of KrF excimer laser beams, in particular, X-rays or electron beams is chemically controlled.
Radiation-sensitive mixtures are conventionally known in themselves. In particular, a positive-type mixture has been commercially used as a resist material containing o-quinonediazide and a binder soluble in an aqueous alkaline solution, such as poly(4-hydroxystyrene) or novolac. However, such a system has insufficient sensitivity and resolving power to radiation, in particular, short-wavelength radiation. Since novolac has a high intrinsic absorption in the UV-2 region (220-300 nm), it is unsuitable as a binder which is used in a single-layer resist material to be exposed to deep UV light (220-300 nm). In contrast, poly(hydroxystyrene) (PHS) is characterized by having more advantageous absorption characteristics in the UV region, higher thermal stability and higher resistance to dry etching.
A positive-type radiation-sensitive mixture for UV-2 in which PHS is used as a binder having a side group sensitive to an acid is known by, for example, U.S. Pat. No. 4,491,628. Further, it is also known that the radiation sensitivity of a radiation-sensitive mixture is enhanced when a compound capable of discharging, by the action of radiation, an acid which has a catalytic action on the secondary reaction is added to the mixture. Examples of the compound which produces a strong acid by the action of radiation include diazonium salts, phosphonium salts, sulfonium salts, iodonium salts, nitrobenzyl esters, phenolic methanesulfonates, diazo compounds, halogen compounds, bissulfonylmethane compounds and bissulfonyldiazomethane compounds.
In the paper "Important Process Parameters in Acetal Deep UV Photoresists" ("Progress in Technique and Treatment of Resists IX" edited by Anthony E. November, Proc. SPIE 1672, 33-45 (1992)), H. Reschelt, et al. describe a positive-type radiation-sensitive mixture which contains a PHS copolymer, a compound capable of generating an acid, and an O-acetal-type oligomerization inhibitor. This photo-sensitive mixture has a shortcoming in that it is extremely sensitive to the non-stableness of an acid latent image. The problem of an unstable acid latent image is an essential problem for a novel resist material which fulfills its function according to the principle of chemical amplification. This problem has been fully discussed in some technical literatures, for example, "Airborne Chemical Contaminants for Chemically-Amplified Resists" by S. A. MacDonald, et al. ("Progress in Technique and Treatment of Resists VIII" edited by Hiroshi Ito, Proc. SPIE 1466, 2-12 (1991)). L. Shlegel presents, in his studies, a problem of diffusion in chemically-amplified resist materials (L. Shlegel, et al., Jap. Journ. of Applied Physics Series 5, presentation at the International Conference on Micro Process in 1991, pp. 175-180). The mean moving range of an acid which acts as a catalyst is equal to the size of a pattern to be resolved in a resist for 240 nm, having high resolving power. In Jap. Journ. of Applied Physics (Vol. 30, No. 10, October, 1991, pp. 2619-2625), J. Nakamura describes a method by which the diffusion length and diffusion constant of an acid in a chemically-amplified resist can be determined. This basic physical phenomenon limits the resolving power in a chemically-amplified system which is particularly sensitive to the change in an acid latent image due to its low barrier to activation energy. The resist described by H. Roschert, et al. in "Progress in Technique and Treatment of Resists IX" edited by Anthony E. November, Proc. SPIE 1672, 33-45 (1992) has the following unfavorable properties due to the problem of diffusion when no additive is used therein:
1) resolving power is only 0.5 micron or less; PA1 2) high resolution can be attained only by the unfavorable deflection of straightness; PA1 3) latitude in exposure is very small; and PA1 4) stability to delay time between exposure and post-exposure baking is extremely poor, and a drastic linewidth change undergoes in a non-exposed resist are. PA1 a) a binder which is insoluble in water but soluble in an aqueous alkaline solution, PA1 b.sup.1) a compound having at least one bond which can be cleaved by an acid, or b.sup.2) a compound having at least one bond which is crosslinked with the compound a) by an acid, PA1 c) a compound which generates an acid when irradiated, and PA1 d) a basic iodonium compound. PA1 Y represents [CH2]n where n is 0 or 1, O or S; PA1 R.sup.3 and R.sup.4 represent C.sub.1 -C.sub.4 alkyl, alkoxy or a halogen; PA1 R.sup.5 and R.sup.6 represent C.sub.1 -C.sub.4 alkyl, alkoxy or a halogen; PA1 X is a basic anion whose pKB value is from -3 to +5; and at least one hydrogen atom of R.sup.1 to R.sup.6 may be substituted by X to form an inner salt; or a mixture of two or more of these compounds is preferably used as the basic iodonium compound d). PA1 1) fully soluble in a resist; PA1 2) having sufficiently high thermal stability; and PA1 3) having a basic counter ion sufficiently. PA1 R.sup.1 and R.sup.2 each independently represent methyl, ethyl, propyl, isopropyl, butyl, phenyl, biphenyl, toluyl, xylyl, chlorophenyl, bromophenyl, methoxyphenyl, ethoxyphenyl, propyloxyphenyl, butyloxyphenyl, tert-butyloxyphenyl, phenoxyphenyl, thiophenoxyphenyl or phenylsulfonylphenyl; PA1 Y represents [CH.sub.2 ].sub.n where n is 0 or 1, O or S; PA1 R.sup.3 and R.sup.4 represent C.sub.1 -C.sub.4 alkyl, methoxy, ethoxy, chlorine or bromine; PA1 R.sup.5 and R.sup.6 represent C.sub.1 -C.sub.4 alkyl, methoxy, ethoxy, chlorine or bromine; PA1 X represents a hydroxyl group, RO.sup.- (R=C.sub.1 -C.sub.4 alkyl), RCOO.sup.- (R=C.sub.1 -C.sub.10 alkyl, aryl, alkylaryl) or OCOO.sup.- ; and at least one hydrogen atom of R.sup.1 to R.sup.6 may be substituted by X to form an inner salt, and X which consist of basic functional group and R may combine with R.sup.1 to R.sup.6 with or without interposing R between the basic functional group and one of R.sup.1 to R.sup.6, such as diphenyliodonium-2-carboxylate. PA1 1) operation can be conducted in the absence of metallic ions; PA1 2) an iodonium salt which is unstable in a separated form can be produced, and used in a radiation-sensitive mixture; and PA1 3) an iodonium salt which cannot be produced in a pure form can be produced, and used in a radiation-sensitive mixture. PA1 R.sup.3 is a C.sub.1 -C.sub.10 alkyl group or an aryl group, PA1 X is --CO--, --O--CO-- or --NH--CO group, and PA1 n is an integer greater than 1. PA1 a heterocyclic aromatic compound represented by the general formula V): ##STR4## in which R.sup.7 and R.sup.9 are an alkyl group, and PA1 R.sup.8 and R.sup.10 are an alkyl group or hydrogen atom, and PA1 Y is the same as X, or hydrogen atom, a C.sub.1 -C.sub.6 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a substituted or unsubstituted or oxygen-, nitrogen- or sulfur-containing C.sub.6 -C.sub.12 aryl, C.sub.6 -C.sub.12 aralkyl or C.sub.6 -C.sub.12 acyl group; PA1 a urethane formaldehyde resin represented by the general formula VI): ##STR5## wherein R.sup.11 is an alkyl group or hydrogen atom; and a crosslinking compound represented by the general formula VII): EQU (R.sup.12 --O--R.sup.14).sub.n --A--(R.sup.14 --O--R.sup.13).sub.mVII) PA1 A is --B--(Z).sub.p -- or --B--Z--B--, in which B is a substituted or unsubstituted, mononuclear aromatic hydrocarbon compound or heterocyclic aromatic compound containing oxygen, sulfur or nitrogen atom, PA1 and Z is direct bond, C.sub.1 -C.sub.4 alkylene, C.sub.1 -C.sub.9 alkylenedioxy or a substituted or unsubstituted phenylene, in which Z may be interrupted by nitrogen atom, --NH--, --O--, --S--, --SO.sub.2 --, --CO--, --CO.sub.2 --, --OCO.sub.2 --, --CONH-- or --O--C.sub.6 H.sub.4 O--; PA1 R.sup.12 and R.sup.13 are hydrogen atom, a C.sub.1 -C.sub.6 alkyl group, a C.sub.1 -C.sub.9 aliphatic unsaturated carbonyl group, a C.sub.5 or C.sub.6 cycloalkyl group, a substituted or unsubstituted C.sub.6 -C.sub.12 aryl, C.sub.6 -C.sub.12 aralkyl or acyl group; PA1 R.sup.14 is a C.sub.1 -C.sub.4 alkylene group in which the chain may be substituted by nitrogen atom, --O--, --CO-- or --CONH--, or a substituted or unsubstituted phenyl; PA1 n is an integer of 1 to 3; PA1 m is an integer of 0 to 3, provided that n+m is at least 2; and PA1 p is an integer of 0 to 3.